The present invention relates to a solid-state imaging apparatus and a manufacturing method thereof, and more particularly to a small-sized solid-state imaging apparatus including a solid-state image pickup element, such as a surveillance camera, a medical camera, or a vehicle camera, and a manufacturing method thereof.
An imaging apparatus of this kind receives an image through an optical system such as a lens, and outputs the image in the form of an electric signal. Recently, in accordance with miniaturization and enhancement of the performance of such an imaging apparatus, also the size of a camera is reduced, and an imaging apparatus is used in various fields and expands its market as an image inputting device.
In a conventional imaging apparatus using a solid-state image pickup element, each of components such as a lens, the solid-state image pickup element, and an LSI on which a driving circuit for the element and a signal processing circuit are mounted, has a shape of a case or a structure member, and the components are combined with each other. Conventionally, a mounting structure based on such a combination is formed by mounting elements onto a flat printed circuit board.
In order to further miniaturize such a device, a three-dimensional printed circuit board 201 shown in FIG. 11 was proposed in Japanese Patent Publication No. 2001-245186. The printed circuit board 201 is made of a resin in which a mounting member is configured by a leg portion 201A having a rectangular table-like shape, and a body portion 201B formed on the leg portion, and a through-opening portion 201C is formed in the interface between the leg portion 201A and the body portion 201B. A printed wiring pattern 205 is formed on the three-dimensional printed circuit board on side of the rear face of the leg portion 201A. A lens is fitted into the inner periphery of the body portion 201B. While being centered at the optical axis 217 of the lens, an optical filter 203 is placed above the through-opening portion 201C, and a solid-state image pickup element 204 and chip components 208 are placed below the through-opening portion. As shown in a section view of FIG. 12, the printed circuit board is connected by using solder 214 through the printed wiring pattern 205 formed on the leg portion 201A, to a main board 213 of an apparatus such as a portable telephone or a personal computer. On the main board 213, formed are a large number of components 219 including chip components such as a signal processing circuit (DSP) which processes an output signal of the solid state imaging element, resistors, and capacitors. Connections among the components are established by connecting the main board 213 to a flexible circuit board (FPC) 120 through a ball grid array (BGA) 221. FIG. 13 is a view showing main portions of the connections. The solid-state image pickup element 204 is connected to the printed wiring pattern 205 formed on the leg portion 201A, through bumps 206 formed on the surface of the image pickup element 204, and then sealed by a sealing resin 207 to accomplish the connections with the three-dimensional printed circuit board 201.
The identical portions are denoted by the identical reference numerals.
As apparent also from the figures, many components must be mounted and then connected to each other. Therefore, a conventional apparatus has problems in that many connections must be formed during a process of mounting components and hence the size of the apparatus is made large, and that the mounting process requires a prolonged time period.
In the mounting process, as shown in FIGS. 14A to 14C, a method is employed in which, after the three-dimensional printed circuit board 201 is molded (FIG. 14A), the solid-state image pickup element 204 is attached to the board (FIG. 14B), and the optical filter 203 is then attached (FIG. 14C).
In a heating step in the process of mounting the solid-state image pickup element 204 onto the three-dimensional printed circuit board 201, the three-dimensional printed circuit board 201 is largely deformed, and a very high stress is generated in connecting portions between the solid-state image pickup element 204 and the three-dimensional printed circuit board 201, so that a connection failure due to cracking often occurs.
Usually, such a three-dimensional printed circuit board is obtained by injection molding. However, there is a problem in that fillers, which are often used in order to reduce the coefficient of expansion of a resin material, cannot be added in an amount larger than a given one from the viewpoints of the molding accuracy and the durability of molding dies.
A thermoplastic resin usually used in injection molding has a straight-chain molecular structure, and hence exhibits anisotropic properties that the coefficient of linear expansion is small in the molecular bonding direction and large in a direction perpendicular to the bonding direction. In such a resin, fillers are oriented in the molding flow direction to exhibit further anisotropic properties that the coefficient is large in a direction perpendicular to the molding flow direction.
As described above, a conventional solid-state imaging apparatus is configured by externally attaching various function components such as a signal processing circuit, and hence has problems in that the mounting process requires a prolonged time period, and that the size of the device is large. Moreover, a connection failure occurs in connecting portions between a solid-state image pickup element and components of a processing circuit, and this causes the reliability to be lowered.
In a heating step in the process of mounting a solid-state image pickup element onto a three-dimensional printed circuit board, the three-dimensional printed circuit board is largely deformed, and a very high stress is generated in connecting portions between the solid-state image pickup element and the three-dimensional printed circuit board, so that a connection failure due to cracking often occurs.
Usually, such connecting portions between a solid-state image pickup element and a three-dimensional printed circuit board are configured by pads disposed on the solid-state image pickup element, and terminals of the three-dimensional printed circuit board. The connection between them is realized by connection using an electrically conductive adhesive agent such as silver paste, ultrasonic bonding, thermocompression bonding, or the like.
In any of the methods, the adhesion of the solid-state image pickup element is easily broken because of thermal deformation of the three-dimensional printed circuit board, and this causes the production yield to be lowered.
When a printed circuit board is three-dimensionally structured, miniaturization is enabled, but thermal distortion is larger than that in the case of a usual two-dimensional structure, thereby causing a large problem in that deformation due to the difference in coefficient of expansion blocks improvement of the yield.
It has been desired to provide a solid-state imaging apparatus which can be easily connected to an external processing circuit, and which can be further miniaturized.